1. Field of the Invention
The present invention relates to a shared-use portable telephone and a method of sharing a portable telephone. More specifically, the present invention relates to a portable telephone that is shared by several persons, appropriately utilizing a telephone directory function of the portable telephone, and a method of sharing such a portable telephone.
2. Description of the Related Art
Japanese Laid Open Patent Application (Heisei 11-215231) discloses a portable type communication terminal such as a portable telephone, which is shared by several persons. As shown in FIG. 1, the portable type communication terminal comprises a CPU 101, a ROM 102 and a RAM 103. The CPU 101 includes a user identifying section 104 that manages two types of information. The first-type information is user identification (ID) code. The second-type information is secret code assigned to the user. The ROM 102 stores a program 105. The RAM 103 includes a personal information storage section 106 and a re-dial number storage section 107.
When one of the users starts authenticating himself, the portable type communication terminal displays an input request message on its LCD section (not shown), requiring the user to input his ID code and secret code. The user inputs his ID code and secret code in response to the input request message. The user identifying section 104 incorporated in the CPU 101 checks whether or not an ID code and a secret code inputted by the user are identical to the user ID code and secret code of the user which are managed by the user identifying section 104. If the ID codes and the secret code inputted by the user are identical to those managed by the user identifying section 104, the personal information and the re-dial number stored in the RAM 103 can be read from the personal information storage section 106 and the re-dial number storage section 107, respectively. Further, the user can write new personal information and a new re-dial number into the personal information storage section 106 and the re-dial number storage section 107, respectively.
When the user finishes authenticating himself or herself, the CPU 101 can write into or read out from the RAM 103 only about management information including the personal information and re-dial number of the user.
In this portable type communication terminal, the data stored in the RAM 103 is erased when all power accumulated in the battery or built-in backup battery, either provided in the portable type communication terminal, is consumed. This is because power is no longer supplied to the RAM 103. Thus, the data stored in the personal information storage section 106 and re-dial number storage section 107 is therefore erased immediately after running out of the battery or the backup battery. Once the ID data stored in the RAM 103 is erased, it is no longer possible for the portable telephone to perform data communication with any switching station and the great influence comes out to operate a system including the portable telephone. In view of this point, the ID data cannot be stored in the RAM 103 of the portable type communication terminal disclosed in Japanese Laid Open Patent Application (Heisei 11-215231).
It is required that each person who can use the portable type communication terminal can access to only the information he or she has right to manage, and share the portable type communication terminal without accessing to the information about any other persons. Also, it is required that the personal information about the persons can not be erased by all means.
Japanese Laid Open Patent Application (Heisei 8-149557) discloses a so-called “cord-less telephone system”, which seems to be related to the present invention. In the cordless telephone system, when any person sharing a mobile station inputs his or her user ID from the mobile station, the user ID thus input is stored into the common user management table that is provided in the main apparatus. When the data showing the condition of the mobile station (whether the station is used by only one person or shared by persons) and the user ID of the person who is holing the station are input, the data showing the condition of the mobile station is stored into the mobile-station condition management table provided in the main apparatus. If the mobile station is used by only one person, the user ID of the person who is holding the mobile station is stored into the shared user management table provided in the main apparatus. The main apparatus comprises switching control means and an extension number management table. To cause the switching control means to determine which user a call should be transmitted to, the main apparatus retrieves the user ID of that person, from the extension number management table. Based on the user ID retrieved, the main apparatus retrieves the mobile station, which registered as the user to be transmitted to, from the common user management table. From the mobile station thus retrieved, the switching control means determines that the call should be transmitted to the mobile station. The call can therefore be transmitted to the mobile station that exists nearer to the user than any other mobile station, no matter whether the mobile station is held by one person or shared by several persons.